An electrophotographic printer has a photosensitive drum with a photoconductive surface layer. In operation, a peripheral surface of the photosensitive drum is uniformly charged, the peripheral surface is exposed through an image of a subject to be copied so as to form an electrostatic latent image thereon, the toner is deposited on the electrostatic latent image for formation of a toner image, and the toner image is copied on a sheet of paper and the like. As shown in FIG. 2, since a toner 2 remains on a peripheral surface of a photosensitive drum 1 after copying, the toner 2 is removed by bringing a distal edge of an elastic cleaning blade 3 into sliding contact with the peripheral surface of the photosensitive drum 1. In the Figure, the cleaning blade 3 is supported by a holding plate 4, and one end of the holding plate 4 (the opposite end to the cleaning blade 3) is fixed on a resin case 5.
The service life of the cleaning blade 3 is determined by physical factors such as abrasion loss and damage through sliding contact, and chemical factors such as stain resistance against toner. A urethane rubber is generally used for formation of the cleaning blade due to its excellent properties against these factors. However, use of the cleaning blade formed of the urethane rubber for a long time causes an remarkable presence of time-course abrasion loss. Therefore, fog (toner is scattered in a non-image portion on a paper sheet), white spot, or the like occur. Accordingly, there have been attempts to enhance the wear resistance of the cleaning blade, such as a method for enhancement of hardness of urethane rubber which is disclosed in Japanese Patent Provisional Publication No. 2-208687.
The cleaning blade obtained according to the above method shows a better effect to some extent, however, the cleaning blade is so hard that it causes damage to the photosensitive drum. In order to enhance the wear resistance, the following methods have been proposed; 1 dispersing a lubricant in urethane rubber (Japanese Patent Provisional Publication No. 7-306616), (2 silicone-modifying urethane rubber (Japanese Patent Provisional publication No.5-224573), 3 providing a coating on a surface of a cured urethane rubber (Japanese Patent Provisional Publication No.4-260084), and 4 breaking the regularity(crystallinity) of a soft segment of the blade (Japanese Patent Provisional Publication No.8-44264). However, in methods 1 to 3, an additional process such as adding a lubricant is required, and in the method 4, the liquid composition for formation of the cleaning blade has a high viscosity, thereby deteriorating processability. In all the above methods, production costs will increase.
On the other hand, a good image forming characteristic is required under an environment of a low temperature as well as ordinary temperature, so that reliability for the electrophotographic printer is enhanced. Thus, it is important that the cleaning blade has a good low temperature cleaning performance.